1. Field of the Invention
This invention relates to a charging member and a process cartridge making use of the same.
2. Description of the Related Art
As a charging member used for contact charging of an electrophotographic photosensitive member, a charging member having a support, a conductive elastic layer provided on the support and an insulative surface layer provided on the conductive elastic layer is in wide use.
Now, the charging member used in such a contact charging system is kept in contact with the photosensitive member, and hence the former's surface may be scraped by any toners, external additives and so forth which remain on the surface of the photosensitive member, so that the toners and toner external additives come to tend to stick to the part having been scrapped. Such a charging member to which the toners and external additives have come to stick partly may cause non-uniform charging on the photosensitive member.
The surface layer may also stand low in electrical resistance at its part having worn, and hence, when the photosensitive member is electrostatically charged by using a charging member having the part having worn, any discharge may localize at that part having worn, to make the surface of the photosensitive member deteriorate as a result thereof.
For such problems, Japanese Patent Application Laid-open No. H08-179591 discloses a method in which an empty space is kept between a charging member and a photosensitive member by providing the former at its each end portion with a spacer member so as to be discharged there. Japanese Patent Application Laid-open No. 2004-020844 also discloses a method in which charge accelerating particles are used to make the surface of a charging member always wear so as to effect stable charging.
Japanese Patent Application Laid-open No. H08-314233 further discloses that a film of urethane resin containing an epichlorohydrin-ethylene oxide copolymer in a proportion of 40% by mass or less has, a high wear resistance and the use of such a film in a charging roller brings an improvement in durability (running performance) of the charging roller.